1. Field of the Invention
This application relates to reduced propellant ammunition cartridges, particularly subsonic cartridges for clandestine use of weapons which normally fire supersonic projectiles.
2. Description of the Prior Art
There is a requirement for subsonic cartridges for clandestine use of weapons which normally fire supersonic projectiles. These subsonic rounds need to work interchangeably with supersonic rounds in so far as they need to fit properly in the same firearm chamber. While it seems it should be an easy job to produce the subsonic rounds by simply reducing the propellant charge until the velocity is adequately reduced, it is known in the art this does not work for a number of reasons.
When the propellant charge becomes small in relation to the total volume within the cartridge case, ignition of the propellant changes with respect to the location of that propellant within the case. Thus, shooting upward with the propellant charge near the primer gives different velocity results than when shooting downward with the propellant charge forward. It is also known that some small charge weights can burn at a very high rate thereby producing chamber pressures above that of full velocity rounds that can cause the cartridge to explode in the weapon with catastrophic results.
Through the years, a number of solutions have been tried which include addition of inert and consumable filler materials as well as addition of expandable inner sleeves that occupy the empty space between the propellant and the projectile, e.g., see U.S. Pat. No. 4,157,684.
The inert and consumable filler materials create problems related with their mass, water retention, combustility and by-products of combustion. Further, they can suffer from inability to keep the propellant from migrating into them due to vibration and handling shocks whereby they have an effect on ignition of the propellant.
The use of expandable inner sleeves limit the production rate in automated loading equipment due to the time it takes the sleeves to expand following insertion and the need to check to assure the sleeve has expanded prior to loading the propellant.
The result of such prior attempts to solve the production of reliable subsonic cartridges has been subsonic rounds that have a larger spread in velocity and thus less accuracy potential than what is desired while associated production costs can be significantly more then full velocity rounds.
Other attempted solutions to the problems associated with the production of subsonic ammunition have been disclosed. For example, see U.S. Pat. No. 5,822,904 which teaches use of stepped down stages in the discharge end of cartridge casings and U.S. Pat. No. 5,770,815 which teaches use of reducing internal casing volume with molded foam fillers as alternative possible solutions.
The present invention provides an improved solution to the subsonic ammunition problems that makes it possible to manufacture better and more price competitive subsonic ammunition then has been possible heretofore.